The invention relates generally to a process and arrangement for the production of steel.
A process for melting scrap, particularly steel scrap, is described in the German Pat. No. 1,800,610. A column of scrap is formed in a melting chamber and a flame is directed at the column from below the same. Here, a centrally positioned, plate-shaped flame is used and the flame extends across the major part of the cross section of the column which latter is of substantially constant cross section. The plate-shaped flame is maintained so far above the bottom of the melting chamber that the melt which flows off is able to form a thermal barrier for the fire-resistant or heat-resistant lining of the melting chamber. The flame is generated by means of a burner lance which is located on the axis of the melting chamber and which extends into the latter either through the top thereof and through the column of scrap or through the bottom of the melting chamber. In this process, the melt which flows off may be introduced directly into a vessel containing molten pig iron in order to be then further processed.
It has been found that optimum melting conditions in the scrap melting chamber are obtained when the flame is produced by the combustion of a stoichiometric oil-oxygen mixture. The characteristics of the melting operation, that is, the oxidizing power of the flame and, concomitantly, the FeO slagging of the charge which occurs during melting, are to be thereby adjusted in accordance with the particular quantity of pig iron in the vessel. The requirement for optimum melting efficiency or, at least, for the minimum possible amount of slagging during melting, necessitates that certain predetermined relationships between the oil and the oxygen be maintained during melting. The difficulties of this process then reside in adjusting the melting characteristics or efficiency in correspondence with the particular quantity of pig iron to be processed.
In oxygen refining processes it is further known to fill relatively large quantities of pig iron, that is, between 70 and 75 percent, into a refining vessel and to then blow with oxygen. The blowing operation generates heat which is sufficient to heat the pig iron to the tapping temperature. In addition, there still remains an excess of heat with which it is possible to melt scrap. In this connection, it has been proposed in the publication "Stahl and Eisen", volume 92, pages 515-518 (1972) to fill molten scrap which has been produced according to the process of the German Pat. No. 1,800,610 into an L-D (Linz-Donawitz) converter. However, by proceeding in this manner, the make-up of the charge is varied solely as a result of the different cooling effects of molten or solid scrap. On the other hand, the iron which becomes slagged during melting of the scrap cannot be recovered in this manner and, in fact, the iron slagging requisite for the formation of a slag must occur anew in the L-D converter.
A refining process is further known from the German Pat. No. 1,074,607 wherein pig iron which has been melted in a pre-melting apparatus is blown in conventional manner in an oxygen converter. The pig iron used here is not produced in a blast furnace but, rather, is produced in a cupola furnace from scrap and coal. The disadvantages outlined above are not eliminated by this process.